Google confessed, "We're aware of a problem with Gmail affecting a significant subset of users. The affected users are able to access Gmail but are seeing error messages, high latency, and/or other unexpected behavior. We will provide an update by 12/15/20, 5:30 PM [Eastern US]detailing when we expect to resolve the problem. Please note that this resolution time is an estimate and may change."
On the internet network administrator outages list, admins reported they were seeing random bounceback issues with an average of 10% bouncebacks on their test emails. Still, other administrators reported seeing bounces when sending from GSuite to consumer Gmail.
Typical bounceback error messages said "The email account that you tried to reach does not exist."
This problem showed up mostly in the US, but it also caused failures in Europe, Australia, and New Zealand.
There have also been scattered reports of trouble with YouTube and YouTube TV, but these have not been confirmed.
At 6:51 PM Eastern, Google reported the Gmail problem had been resolved. The company also stated: "We apologize for the inconvenience and thank you for your patience and continued support. Please rest assured that system reliability is a top priority at Google, and we are making continuous improvements to make our systems better. If you are still experiencing an issue, please contact us via the Google Help Center."